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Fully Metal-Coated Scanning Near-Field Optical Microscopy Probes with Spiral Corrugations for Superfocusing under Arbitrarily Oriented Linearly Polarised Excitation.

Lotito V, Sennhauser U, Hafner C, Bona GL - Plasmonics (2011)

Bottom Line: We study the effect of a spiral corrugation on the outer surface of a fully metal-coated scanning near-field optical microscopy (SNOM) probe using the finite element method.The introduction of a novel form of asymmetry, devoid of any preferential spatial direction and covering the whole angular range of the originally axisymmetric tip, allows attaining strong field localization for a linearly polarised mode with arbitrary orientation.Compared to previously proposed asymmetric structures which require linearly polarised excitation properly oriented with respect to the asymmetry, such a configuration enables significant simplification in mode injection.

View Article: PubMed Central - PubMed

ABSTRACT
We study the effect of a spiral corrugation on the outer surface of a fully metal-coated scanning near-field optical microscopy (SNOM) probe using the finite element method. The introduction of a novel form of asymmetry, devoid of any preferential spatial direction and covering the whole angular range of the originally axisymmetric tip, allows attaining strong field localization for a linearly polarised mode with arbitrary orientation. Compared to previously proposed asymmetric structures which require linearly polarised excitation properly oriented with respect to the asymmetry, such a configuration enables significant simplification in mode injection. In fact, not only is the need for the delicate procedure to generate radially polarised beams overcome, but also the relative alignment between the linearly polarised beam and the tip modification is no longer critical.

No MeSH data available.


Characteristics of the near-field intensity distributions for variable filling material and variable radius of the spiral corrugation under linearly polarised excitation (H and V): a average value of the ratio between the peak value for the probe with spiral corrugation and the one of the standard reference probe under radially polarised excitation; b average value of the FWHM; c maximum deviation from the average value of the ratio between the peak value for the probe with spiral corrugation and the one of the standard reference probe under radially polarised excitation; d maximum deviation from the average value of the FWHM
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Fig5: Characteristics of the near-field intensity distributions for variable filling material and variable radius of the spiral corrugation under linearly polarised excitation (H and V): a average value of the ratio between the peak value for the probe with spiral corrugation and the one of the standard reference probe under radially polarised excitation; b average value of the FWHM; c maximum deviation from the average value of the ratio between the peak value for the probe with spiral corrugation and the one of the standard reference probe under radially polarised excitation; d maximum deviation from the average value of the FWHM

Mentions: Both the FWHM and the peak value can be tuned and optimised by changing the characteristics of the spiral corrugation. As anticipated, an indentation can be used instead of a metal protrusion, that is the metal can be carved in a spiral shape, or, as an alternative, another dielectric such as aluminium oxide (n = 1.54) can fill the spiral corrugation. In fact, the coupling between surface modes at two adjacent metal/dielectric interfaces can be modulated by changing the indices of refraction of the dielectric materials [25]. Additionally, the radius of the spiral r can be changed to get stronger or weaker asymmetries. This geometric parameter was varied from 15 to 30 nm with a step of 5 nm. More specifically, for each structure based on a particular combination of filling material and radius r, we undertook an analysis similar to the one shown in the previous paragraph for the spiral metal corrugation of radius r = 25 nm, that is we rotated the corrugation from −40° to 45° with a step of 5°. Then, we calculated the average value of the peak ratio and the FWHM for the linearly polarised distributions over all the rotated positions, as explained in the previous paragraph, and considered these values together with the maximum deviation from the corresponding average as figures of merit for comparison. The results for the three different filling materials as a function of the radius r are reported in Fig. 5.Fig. 5


Fully Metal-Coated Scanning Near-Field Optical Microscopy Probes with Spiral Corrugations for Superfocusing under Arbitrarily Oriented Linearly Polarised Excitation.

Lotito V, Sennhauser U, Hafner C, Bona GL - Plasmonics (2011)

Characteristics of the near-field intensity distributions for variable filling material and variable radius of the spiral corrugation under linearly polarised excitation (H and V): a average value of the ratio between the peak value for the probe with spiral corrugation and the one of the standard reference probe under radially polarised excitation; b average value of the FWHM; c maximum deviation from the average value of the ratio between the peak value for the probe with spiral corrugation and the one of the standard reference probe under radially polarised excitation; d maximum deviation from the average value of the FWHM
© Copyright Policy
Related In: Results  -  Collection

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Fig5: Characteristics of the near-field intensity distributions for variable filling material and variable radius of the spiral corrugation under linearly polarised excitation (H and V): a average value of the ratio between the peak value for the probe with spiral corrugation and the one of the standard reference probe under radially polarised excitation; b average value of the FWHM; c maximum deviation from the average value of the ratio between the peak value for the probe with spiral corrugation and the one of the standard reference probe under radially polarised excitation; d maximum deviation from the average value of the FWHM
Mentions: Both the FWHM and the peak value can be tuned and optimised by changing the characteristics of the spiral corrugation. As anticipated, an indentation can be used instead of a metal protrusion, that is the metal can be carved in a spiral shape, or, as an alternative, another dielectric such as aluminium oxide (n = 1.54) can fill the spiral corrugation. In fact, the coupling between surface modes at two adjacent metal/dielectric interfaces can be modulated by changing the indices of refraction of the dielectric materials [25]. Additionally, the radius of the spiral r can be changed to get stronger or weaker asymmetries. This geometric parameter was varied from 15 to 30 nm with a step of 5 nm. More specifically, for each structure based on a particular combination of filling material and radius r, we undertook an analysis similar to the one shown in the previous paragraph for the spiral metal corrugation of radius r = 25 nm, that is we rotated the corrugation from −40° to 45° with a step of 5°. Then, we calculated the average value of the peak ratio and the FWHM for the linearly polarised distributions over all the rotated positions, as explained in the previous paragraph, and considered these values together with the maximum deviation from the corresponding average as figures of merit for comparison. The results for the three different filling materials as a function of the radius r are reported in Fig. 5.Fig. 5

Bottom Line: We study the effect of a spiral corrugation on the outer surface of a fully metal-coated scanning near-field optical microscopy (SNOM) probe using the finite element method.The introduction of a novel form of asymmetry, devoid of any preferential spatial direction and covering the whole angular range of the originally axisymmetric tip, allows attaining strong field localization for a linearly polarised mode with arbitrary orientation.Compared to previously proposed asymmetric structures which require linearly polarised excitation properly oriented with respect to the asymmetry, such a configuration enables significant simplification in mode injection.

View Article: PubMed Central - PubMed

ABSTRACT
We study the effect of a spiral corrugation on the outer surface of a fully metal-coated scanning near-field optical microscopy (SNOM) probe using the finite element method. The introduction of a novel form of asymmetry, devoid of any preferential spatial direction and covering the whole angular range of the originally axisymmetric tip, allows attaining strong field localization for a linearly polarised mode with arbitrary orientation. Compared to previously proposed asymmetric structures which require linearly polarised excitation properly oriented with respect to the asymmetry, such a configuration enables significant simplification in mode injection. In fact, not only is the need for the delicate procedure to generate radially polarised beams overcome, but also the relative alignment between the linearly polarised beam and the tip modification is no longer critical.

No MeSH data available.